Processor prefetch throttling based on short streams

ABSTRACT

In an embodiment, a processor comprises a prefetch history array and a prefetch circuit. The prefetch history array comprises a plurality of entries corresponding to prefetch addresses, each entry of the plurality of entries comprising a sublength value associated with a frequency that a stride is repeated. The prefetch circuit is to: for each entry of the plurality of entries, adjust the sublength value based on stride matches for an address of the entry; adjust a short stream counter based on the sublength values of the plurality of entries in the prefetch history array; determine whether the short stream counter has exceeded a throttling threshold; and in response to a determination that the short stream counter has exceeded the throttling threshold, throttle a prefetch level of the prefetch circuit. Other embodiments are described and claimed.

FIELD OF INVENTION

Embodiments relate to computer processors, and more particularly toprefetching in computer processors.

BACKGROUND

Computing devices may include a central processor and main memory (e.g.,random-access memory external to the processor). The processor may readdata and instructions from the main memory, and may write executionresults to the main memory. If the information that will be used by theprocessor can be predicted, then such information can be prefetched tobe available to the processor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a portion of a system in accordance with anembodiment of the present invention.

FIG. 2 is a block diagram of a processor in accordance with anembodiment of the present invention.

FIG. 3 is a block diagram of a multi-domain processor in accordance withanother embodiment of the present invention.

FIG. 4 is an embodiment of a processor including multiple cores.

FIG. 5 is a block diagram of a micro-architecture of a processor core inaccordance with one embodiment of the present invention.

FIG. 6 is a block diagram of a micro-architecture of a processor core inaccordance with another embodiment.

FIG. 7 is a block diagram of a micro-architecture of a processor core inaccordance with yet another embodiment.

FIG. 8 is a block diagram of a micro-architecture of a processor core inaccordance with a still further embodiment.

FIG. 9 is a block diagram of a processor in accordance with anotherembodiment of the present invention.

FIG. 10 is a block diagram of a representative SoC in accordance with anembodiment of the present invention.

FIG. 11 is a block diagram of another example SoC in accordance with anembodiment of the present invention.

FIG. 12 is a block diagram of an example system with which embodimentscan be used.

FIG. 13 is a block diagram of another example system with whichembodiments may be used.

FIG. 14 is a block diagram of a representative computer system.

FIG. 15 is a block diagram of a system in accordance with an embodimentof the present invention.

FIG. 16 is a block diagram illustrating an IP core development systemused to manufacture an integrated circuit to perform operationsaccording to an embodiment.

FIG. 17 is a diagram of an example system for prefetch throttling inaccordance with one or more embodiments.

FIG. 18 is a diagram of an example prefetch history array in accordancewith one or more embodiments.

FIG. 19 is an example prefetch state machine in accordance with one ormore embodiments.

FIG. 20 is a flow diagram of an example method for prefetch throttlingin accordance with one or more embodiments.

FIG. 21 is a flow diagram of an example method for prefetch throttlingin accordance with one or more embodiments.

DETAILED DESCRIPTION

Prefetching is a technique for improving processor performance. However,overly aggressive prefetching may waste time and energy if theprefetched lines are not used by the processor. In accordance with someembodiments, a prefetch circuit of a processor may be throttled based oninformation about short stream patterns. In some embodiments, a globalshort stream counter may be used to smooth information about streamsublengths over time, and to determine an amount of throttling of theprefetch circuit. In accordance with one or more embodiments, the numberof unused prefetches may be reduced. Accordingly, some embodiments mayreduce energy and bandwidth consumption of processors, systems,platforms, and so forth.

Although the following embodiments are described with reference tospecific integrated circuits, such as in computing platforms orprocessors, other embodiments are applicable to other types ofintegrated circuits and logic devices. Similar techniques and teachingsof embodiments described herein may be applied to other types ofcircuits or semiconductor devices. For example, the disclosedembodiments are not limited to any particular type of computer systems.That is, disclosed embodiments can be used in many different systemtypes, ranging from server computers (e.g., tower, rack, blade,micro-server and so forth), communications systems, storage systems,desktop computers of any configuration, laptop, notebook, and tabletcomputers (including 2:1 tablets, phablets and so forth), and may bealso used in other devices, such as handheld devices, systems on chip(SoCs), and embedded applications. Some examples of handheld devicesinclude cellular phones such as smartphones, Internet protocol devices,digital cameras, personal digital assistants (PDAs), and handheld PCs.Embedded applications may typically include a microcontroller, a digitalsignal processor (DSP), network computers (NetPC), set-top boxes,network hubs, wide area network (WAN) switches, wearable devices, or anyother system that can perform the functions and operations taught below.More so, embodiments may be implemented in mobile terminals havingstandard voice functionality such as mobile phones, smartphones andphablets, and/or in non-mobile terminals without a standard wirelessvoice function communication capability, such as many wearables,tablets, notebooks, desktops, micro-servers, servers and so forth.Moreover, the apparatuses, methods, and systems described herein are notlimited to physical computing devices, but may also relate to softwareimplementations.

Referring now to FIG. 1, shown is a block diagram of a portion of asystem in accordance with an embodiment of the present invention. Asshown in FIG. 1, system 100 may include various components, including aprocessor 110 which as shown is a multicore processor. Processor 110 maybe coupled to a power supply 150 via an external voltage regulator 160,which may perform a first voltage conversion to provide a primaryregulated voltage Vreg to processor 110.

As seen, processor 110 may be a single die processor including multiplecores 120 a-120 n. In addition, each core may be associated with anintegrated voltage regulator (IVR) 125 a-125 n which receives theprimary regulated voltage and generates an operating voltage to beprovided to one or more agents of the processor associated with the IVR.Accordingly, an IVR implementation may be provided to allow forfine-grained control of voltage and thus power and performance of eachindividual core. As such, each core can operate at an independentvoltage and frequency, enabling great flexibility and affording wideopportunities for balancing power consumption with performance. In someembodiments, the use of multiple IVRs enables the grouping of componentsinto separate power planes, such that power is regulated and supplied bythe IVR to only those components in the group. During power management,a given power plane of one IVR may be powered down or off when theprocessor is placed into a certain low power state, while another powerplane of another IVR remains active, or fully powered. Similarly, cores120 may include or be associated with independent clock generationcircuitry such as one or more phase lock loops (PLLs) to controloperating frequency of each core 120 independently.

Still referring to FIG. 1, additional components may be present withinthe processor including an input/output interface (IF) 132, anotherinterface 134, and an integrated memory controller (IMC) 136. As seen,each of these components may be powered by another integrated voltageregulator 125 _(x). In one embodiment, interface 132 may enableoperation for an Intel® Quick Path Interconnect (QPI) interconnect,which provides for point-to-point (PtP) links in a cache coherentprotocol that includes multiple layers including a physical layer, alink layer and a protocol layer. In turn, interface 134 may communicatevia a Peripheral Component Interconnect Express (PCIe™) protocol.

Also shown is a power control unit (PCU) 138, which may includecircuitry including hardware, software and/or firmware to perform powermanagement operations with regard to processor 110. As seen, PCU 138provides control information to external voltage regulator 160 via adigital interface 162 to cause the voltage regulator to generate theappropriate regulated voltage. PCU 138 also provides control informationto IVRs 125 via another digital interface 163 to control the operatingvoltage generated (or to cause a corresponding IVR to be disabled in alow power mode). In various embodiments, PCU 138 may include a varietyof power management logic units to perform hardware-based powermanagement. Such power management may be wholly processor controlled(e.g., by various processor hardware, and which may be triggered byworkload and/or power, thermal or other processor constraints) and/orthe power management may be performed responsive to external sources(such as a platform or power management source or system software).

In FIG. 1, PCU 138 is illustrated as being present as a separate logicof the processor. In other cases PCU logic 138 may execute on a givenone or more of cores 120. In some cases, PCU 138 may be implemented as amicrocontroller (dedicated or general-purpose) or other control logicconfigured to execute its own dedicated power management code, sometimesreferred to as P-code. In yet other embodiments, power managementoperations to be performed by PCU 138 may be implemented externally to aprocessor, such as by way of a separate power management integratedcircuit (PMIC) or other component external to the processor. In yetother embodiments, power management operations to be performed by PCU138 may be implemented within BIOS or other system software.

Embodiments may be particularly suitable for a multicore processor inwhich each of multiple cores can operate at an independent voltage andfrequency point. As used herein the term “domain” is used to mean acollection of hardware and/or logic that operates at the same voltageand frequency point. In addition, a multicore processor can furtherinclude other non-core processing engines such as fixed function units,graphics engines, and so forth. Such processor can include independentdomains other than the cores, such as one or more domains associatedwith a graphics engine (referred to herein as a graphics domain) and oneor more domains associated with non-core circuitry, referred to hereinas an uncore or a system agent. Although many implementations of amulti-domain processor can be formed on a single semiconductor die,other implementations can be realized by a multi-chip package in whichdifferent domains can be present on different semiconductor die of asingle package.

While not shown for ease of illustration, understand that additionalcomponents may be present within processor 110 such as uncore logic, andother components such as internal memories, e.g., one or more levels ofa cache memory hierarchy and so forth. Furthermore, while shown in theimplementation of FIG. 1 with an integrated voltage regulator,embodiments are not so limited. For example, other regulated voltagesmay be provided to on-chip resources from external voltage regulator 160or one or more additional external sources of regulated voltages.

Note that the power management techniques described herein may beindependent of and complementary to an operating system (OS)-based powermanagement (OSPM) mechanism. According to one example OSPM technique, aprocessor can operate at various performance states or levels, so-calledP-states, namely from P0 to PN. In general, the P1 performance state maycorrespond to the highest guaranteed performance state that can berequested by an OS. In addition to this P1 state, the OS can furtherrequest a higher performance state, namely a P0 state. This P0 state maythus be an opportunistic, overclocking, or turbo mode state in which,when power and/or thermal budget is available, processor hardware canconfigure the processor or at least portions thereof to operate at ahigher than guaranteed frequency. In many implementations a processorcan include multiple so-called bin frequencies above the P1 guaranteedmaximum frequency, exceeding to a maximum peak frequency of theparticular processor, as fused or otherwise written into the processorduring manufacture. In addition, according to one OSPM mechanism, aprocessor can operate at various power states or levels. With regard topower states, an OSPM mechanism may specify different power consumptionstates, generally referred to as C-states, C0, C1 to Cn states. When acore is active, it runs at a C0 state, and when the core is idle it maybe placed in a core low power state, also called a core non-zero C-state(e.g., C1-C6 states), with each C-state being at a lower powerconsumption level (such that C6 is a deeper low power state than C1, andso forth).

Understand that many different types of power management techniques maybe used individually or in combination in different embodiments. Asrepresentative examples, a power controller may control the processor tobe power managed by some form of dynamic voltage frequency scaling(DVFS) in which an operating voltage and/or operating frequency of oneor more cores or other processor logic may be dynamically controlled toreduce power consumption in certain situations. In an example, DVFS maybe performed using Enhanced Intel SpeedStep™ technology available fromIntel Corporation, Santa Clara, Calif., to provide optimal performanceat a lowest power consumption level. In another example, DVFS may beperformed using Intel TurboBoost™ technology to enable one or more coresor other compute engines to operate at a higher than guaranteedoperating frequency based on conditions (e.g., workload andavailability).

Another power management technique that may be used in certain examplesis dynamic swapping of workloads between different compute engines. Forexample, the processor may include asymmetric cores or other processingengines that operate at different power consumption levels, such that ina power constrained situation, one or more workloads can be dynamicallyswitched to execute on a lower power core or other compute engine.Another exemplary power management technique is hardware duty cycling(HDC), which may cause cores and/or other compute engines to beperiodically enabled and disabled according to a duty cycle, such thatone or more cores may be made inactive during an inactive period of theduty cycle and made active during an active period of the duty cycle.

Power management techniques also may be used when constraints exist inan operating environment. For example, when a power and/or thermalconstraint is encountered, power may be reduced by reducing operatingfrequency and/or voltage. Other power management techniques includethrottling instruction execution rate or limiting scheduling ofinstructions. Still further, it is possible for instructions of a giveninstruction set architecture to include express or implicit direction asto power management operations. Although described with these particularexamples, understand that many other power management techniques may beused in particular embodiments.

Embodiments can be implemented in processors for various marketsincluding server processors, desktop processors, mobile processors andso forth. Referring now to FIG. 2, shown is a block diagram of aprocessor in accordance with an embodiment of the present invention. Asshown in FIG. 2, processor 200 may be a multicore processor including aplurality of cores 210 _(a)-210 _(a). In one embodiment, each such coremay be of an independent power domain and can be configured to enter andexit active states and/or maximum performance states based on workload.One or more cores 210 may be heterogeneous to the other cores, e.g.,having different micro-architectures, instruction set architectures,pipeline depths, power and performance capabilities. The various coresmay be coupled via an interconnect 215 to a system agent or uncore 220that includes various components. As seen, the uncore 220 may include ashared cache 230 which may be a last level cache. In addition, theuncore may include an integrated memory controller 240 to communicatewith a system memory (not shown in FIG. 2), e.g., via a memory bus.Uncore 220 also includes various interfaces 250 and a power control unit255, which may include logic to perform the power management techniquesdescribed herein.

In addition, by interfaces 250 a-250 n, connection can be made tovarious off-chip components such as peripheral devices, mass storage andso forth. While shown with this particular implementation in theembodiment of FIG. 2, the scope of the present invention is not limitedin this regard.

Referring now to FIG. 3, shown is a block diagram of a multi-domainprocessor in accordance with another embodiment of the presentinvention. As shown in the embodiment of FIG. 3, processor 300 includesmultiple domains. Specifically, a core domain 310 can include aplurality of cores 310 a-310 n, a graphics domain 320 can include one ormore graphics engines, and a system agent domain 350 may further bepresent. In some embodiments, system agent domain 350 may execute at anindependent frequency than the core domain and may remain powered on atall times to handle power control events and power management such thatdomains 310 and 320 can be controlled to dynamically enter into and exithigh power and low power states. Each of domains 310 and 320 may operateat different voltage and/or power. Note that while only shown with threedomains, understand the scope of the present invention is not limited inthis regard and additional domains can be present in other embodiments.For example, multiple core domains may be present each including atleast one core.

In general, each core 310 may further include low level caches inaddition to various execution units and additional processing elements.In turn, the various cores may be coupled to each other and to a sharedcache memory formed of a plurality of units of a last level cache (LLC)340 a-340 n. In various embodiments, LLC 340 may be shared amongst thecores and the graphics engine, as well as various media processingcircuitry. As seen, a ring interconnect 330 thus couples the corestogether, and provides interconnection between the cores, graphicsdomain 320 and system agent circuitry 350. In one embodiment,interconnect 330 can be part of the core domain. However in otherembodiments the ring interconnect can be of its own domain.

As further seen, system agent domain 350 may include display controller352 which may provide control of and an interface to an associateddisplay. As further seen, system agent domain 350 may include a powercontrol unit 355 which can include logic to perform the power managementtechniques described herein.

As further seen in FIG. 3, processor 300 can further include anintegrated memory controller (IMC) 370 that can provide for an interfaceto a system memory, such as a dynamic random access memory (DRAM).Multiple interfaces 380 a-380 n may be present to enable interconnectionbetween the processor and other circuitry. For example, in oneembodiment at least one direct media interface (DMI) interface may beprovided as well as one or more PCIe™ interfaces. Still further, toprovide for communications between other agents such as additionalprocessors or other circuitry, one or more QPI interfaces may also beprovided. Although shown at this high level in the embodiment of FIG. 3,understand the scope of the present invention is not limited in thisregard.

Referring to FIG. 4, an embodiment of a processor including multiplecores is illustrated. Processor 400 includes any processor or processingdevice, such as a microprocessor, an embedded processor, a digitalsignal processor (DSP), a network processor, a handheld processor, anapplication processor, a co-processor, a system on a chip (SoC), orother device to execute code. Processor 400, in one embodiment, includesat least two cores—cores 401 and 402, which may include asymmetric coresor symmetric cores (the illustrated embodiment). However, processor 400may include any number of processing elements that may be symmetric orasymmetric.

In one embodiment, a processing element refers to hardware or logic tosupport a software thread. Examples of hardware processing elementsinclude: a thread unit, a thread slot, a thread, a process unit, acontext, a context unit, a logical processor, a hardware thread, a core,and/or any other element, which is capable of holding a state for aprocessor, such as an execution state or architectural state. In otherwords, a processing element, in one embodiment, refers to any hardwarecapable of being independently associated with code, such as a softwarethread, operating system, application, or other code. A physicalprocessor typically refers to an integrated circuit, which potentiallyincludes any number of other processing elements, such as cores orhardware threads.

A core often refers to logic located on an integrated circuit capable ofmaintaining an independent architectural state, wherein eachindependently maintained architectural state is associated with at leastsome dedicated execution resources. In contrast to cores, a hardwarethread typically refers to any logic located on an integrated circuitcapable of maintaining an independent architectural state, wherein theindependently maintained architectural states share access to executionresources. As can be seen, when certain resources are shared and othersare dedicated to an architectural state, the line between thenomenclature of a hardware thread and core overlaps. Yet often, a coreand a hardware thread are viewed by an operating system as individuallogical processors, where the operating system is able to individuallyschedule operations on each logical processor.

Physical processor 400, as illustrated in FIG. 4, includes two cores,cores 401 and 402. Here, cores 401 and 402 are considered symmetriccores, i.e., cores with the same configurations, functional units,and/or logic. In another embodiment, core 401 includes an out-of-orderprocessor core, while core 402 includes an in-order processor core.However, cores 401 and 402 may be individually selected from any type ofcore, such as a native core, a software managed core, a core adapted toexecute a native instruction set architecture (ISA), a core adapted toexecute a translated ISA, a co-designed core, or other known core. Yetto further the discussion, the functional units illustrated in core 401are described in further detail below, as the units in core 402 operatein a similar manner.

As depicted, core 401 includes two hardware threads 401 a and 401 b,which may also be referred to as hardware thread slots 401 a and 401 b.Therefore, software entities, such as an operating system, in oneembodiment potentially view processor 400 as four separate processors,i.e., four logical processors or processing elements capable ofexecuting four software threads concurrently. As alluded to above, afirst thread is associated with architecture state registers 401 a, asecond thread is associated with architecture state registers 401 b, athird thread may be associated with architecture state registers 402 a,and a fourth thread may be associated with architecture state registers402 b. Here, each of the architecture state registers (401 a, 401 b, 402a, and 402 b) may be referred to as processing elements, thread slots,or thread units, as described above. As illustrated, architecture stateregisters 401 a are replicated in architecture state registers 401 b, soindividual architecture states/contexts are capable of being stored forlogical processor 401 a and logical processor 401 b. In core 401, othersmaller resources, such as instruction pointers and renaming logic inallocator and renamer block 430 may also be replicated for threads 401 aand 401 b. Some resources, such as re-order buffers inreorder/retirement unit 435, branch target buffer and instructiontranslation lookaside buffer (BTB and I-TLB) 420, load/store buffers,and queues may be shared through partitioning. Other resources, such asgeneral purpose internal registers, page-table base register(s),low-level data-cache and data-TLB 450, execution unit(s) 440, andportions of out-of-order unit 435 are potentially fully shared.

Processor 400 often includes other resources, which may be fully shared,shared through partitioning, or dedicated by/to processing elements. InFIG. 4, an embodiment of a purely exemplary processor with illustrativelogical units/resources of a processor is illustrated. Note that aprocessor may include, or omit, any of these functional units, as wellas include any other known functional units, logic, or firmware notdepicted. As illustrated, core 401 includes a simplified, representativeout-of-order (OOO) processor core. But an in-order processor may beutilized in different embodiments. The OOO core includes a branch targetbuffer 420 to predict branches to be executed/taken and aninstruction-translation buffer (I-TLB) 420 to store address translationentries for instructions.

Core 401 further includes decode module 425 coupled to a fetch unit todecode fetched elements. Fetch logic, in one embodiment, includesindividual sequencers associated with thread slots 401 a, 401 b,respectively. Usually core 401 is associated with a first ISA, whichdefines/specifies instructions executable on processor 400. Oftenmachine code instructions that are part of the first ISA include aportion of the instruction (referred to as an opcode), whichreferences/specifies an instruction or operation to be performed. Decodelogic 425 includes circuitry that recognizes these instructions fromtheir opcodes and passes the decoded instructions on in the pipeline forprocessing as defined by the first ISA. For example, decoders 425, inone embodiment, include logic designed or adapted to recognize specificinstructions, such as transactional instruction. As a result of therecognition by decoders 425, the architecture or core 401 takesspecific, predefined actions to perform tasks associated with theappropriate instruction. It is important to note that any of the tasks,blocks, operations, and methods described herein may be performed inresponse to a single or multiple instructions; some of which may be newor old instructions.

In one example, allocator and renamer block 430 includes an allocator toreserve resources, such as register files to store instructionprocessing results. However, threads 401 a and 401 b are potentiallycapable of out-of-order execution, where allocator and renamer block 430also reserves other resources, such as reorder buffers to trackinstruction results. Unit 430 may also include a register renamer torename program/instruction reference registers to other registersinternal to processor 400. Reorder/retirement unit 435 includescomponents, such as the reorder buffers mentioned above, load buffers,and store buffers, to support out-of-order execution and later in-orderretirement of instructions executed out-of-order.

Scheduler and execution unit(s) block 440, in one embodiment, includes ascheduler unit to schedule instructions/operation on execution units.For example, a floating point instruction is scheduled on a port of anexecution unit that has an available floating point execution unit.Register files associated with the execution units are also included tostore information instruction processing results. Exemplary executionunits include a floating point execution unit, an integer executionunit, a jump execution unit, a load execution unit, a store executionunit, and other known execution units.

Lower level data cache and data translation lookaside buffer (D-TLB) 450are coupled to execution unit(s) 440. The data cache is to storerecently used/operated on elements, such as data operands, which arepotentially held in memory coherency states. The D-TLB is to storerecent virtual/linear to physical address translations. As a specificexample, a processor may include a page table structure to breakphysical memory into a plurality of virtual pages.

Here, cores 401 and 402 share access to higher-level or further-outcache 410, which is to cache recently fetched elements. Note thathigher-level or further-out refers to cache levels increasing or gettingfurther away from the execution unit(s). In one embodiment, higher-levelcache 410 is a last-level data cache—last cache in the memory hierarchyon processor 400—such as a second or third level data cache. However,higher level cache 410 is not so limited, as it may be associated withor includes an instruction cache. A trace cache—a type of instructioncache—instead may be coupled after decoder 425 to store recently decodedtraces.

In the depicted configuration, processor 400 also includes bus interfacemodule 405 and a power control unit 460, which may perform powermanagement in accordance with an embodiment of the present invention. Inthis scenario, bus interface 405 is to communicate with devices externalto processor 400, such as system memory and other components.

A memory controller 470 may interface with other devices such as one ormany memories. In an example, bus interface 405 includes a ringinterconnect with a memory controller for interfacing with a memory anda graphics controller for interfacing with a graphics processor. In anSoC environment, even more devices, such as a network interface,coprocessors, memory, graphics processor, and any other known computerdevices/interface may be integrated on a single die or integratedcircuit to provide small form factor with high functionality and lowpower consumption.

Referring now to FIG. 5, shown is a block diagram of amicro-architecture of a processor core in accordance with one embodimentof the present invention. As shown in FIG. 5, processor core 500 may bea multi-stage pipelined out-of-order processor. Core 500 may operate atvarious voltages based on a received operating voltage, which may bereceived from an integrated voltage regulator or external voltageregulator.

As seen in FIG. 5, core 500 includes front end units 510, which may beused to fetch instructions to be executed and prepare them for use laterin the processor pipeline. For example, front end units 510 may includea fetch unit 501, an instruction cache 503, and an instruction decoder505. In some implementations, front end units 510 may further include atrace cache, along with microcode storage as well as a micro-operationstorage. Fetch unit 501 may fetch macro-instructions, e.g., from memoryor instruction cache 503, and feed them to instruction decoder 505 todecode them into primitives, i.e., micro-operations for execution by theprocessor.

Coupled between front end units 510 and execution units 520 is anout-of-order (OOO) engine 515 that may be used to receive themicro-instructions and prepare them for execution. More specifically OOOengine 515 may include various buffers to re-order micro-instructionflow and allocate various resources needed for execution, as well as toprovide renaming of logical registers onto storage locations withinvarious register files such as register file 530 and extended registerfile 535. Register file 530 may include separate register files forinteger and floating point operations. For purposes of configuration,control, and additional operations, a set of machine specific registers(MSRs) 538 may also be present and accessible to various logic withincore 500 (and external to the core).

Various resources may be present in execution units 520, including, forexample, various integer, floating point, and single instructionmultiple data (SIMD) logic units, among other specialized hardware. Forexample, such execution units may include one or more arithmetic logicunits (ALUs) 522 and one or more vector execution units 524, among othersuch execution units.

Results from the execution units may be provided to retirement logic,namely a reorder buffer (ROB) 540. More specifically, ROB 540 mayinclude various arrays and logic to receive information associated withinstructions that are executed. This information is then examined by ROB540 to determine whether the instructions can be validly retired andresult data committed to the architectural state of the processor, orwhether one or more exceptions occurred that prevent a proper retirementof the instructions. Of course, ROB 540 may handle other operationsassociated with retirement.

As shown in FIG. 5, ROB 540 is coupled to a cache 550 which, in oneembodiment may be a low level cache (e.g., an L1 cache) although thescope of the present invention is not limited in this regard. Also,execution units 520 can be directly coupled to cache 550. From cache550, data communication may occur with higher level caches, systemmemory and so forth. While shown with this high level in the embodimentof FIG. 5, understand the scope of the present invention is not limitedin this regard. For example, while the implementation of FIG. 5 is withregard to an out-of-order machine such as of an Intel® x86 instructionset architecture (ISA), the scope of the present invention is notlimited in this regard. That is, other embodiments may be implemented inan in-order processor, a reduced instruction set computing (RISC)processor such as an ARM-based processor, or a processor of another typeof ISA that can emulate instructions and operations of a different ISAvia an emulation engine and associated logic circuitry.

Referring now to FIG. 6, shown is a block diagram of amicro-architecture of a processor core in accordance with anotherembodiment. In the embodiment of FIG. 6, core 600 may be a low powercore of a different micro-architecture, such as an Intel® Atom™-basedprocessor having a relatively limited pipeline depth designed to reducepower consumption. As seen, core 600 includes an instruction cache 610coupled to provide instructions to an instruction decoder 615. A branchpredictor 605 may be coupled to instruction cache 610. Note thatinstruction cache 610 may further be coupled to another level of a cachememory, such as an L2 cache (not shown for ease of illustration in FIG.6). In turn, instruction decoder 615 provides decoded instructions to anissue queue (IQ) 620 for storage and delivery to a given executionpipeline. A microcode ROM 618 is coupled to instruction decoder 615.

A floating point pipeline 630 includes a floating point (FP) registerfile 632 which may include a plurality of architectural registers of agiven bit width such as 128, 256 or 512 bits. Pipeline 630 includes afloating point scheduler 634 to schedule instructions for execution onone of multiple execution units of the pipeline. In the embodimentshown, such execution units include an ALU 635, a shuffle unit 636, anda floating point adder 638. In turn, results generated in theseexecution units may be provided back to buffers and/or registers ofregister file 632. Of course understand while shown with these fewexample execution units, additional or different floating pointexecution units may be present in another embodiment.

An integer pipeline 640 also may be provided. In the embodiment shown,pipeline 640 includes an integer (INT) register file 642 which mayinclude a plurality of architectural registers of a given bit width suchas 128 or 256 bits. Pipeline 640 includes an integer execution (IE)scheduler 644 to schedule instructions for execution on one of multipleexecution units of the pipeline. In the embodiment shown, such executionunits include an ALU 645, a shifter unit 646, and a jump execution unit(JEU) 648. In turn, results generated in these execution units may beprovided back to buffers and/or registers of register file 642. Ofcourse understand while shown with these few example execution units,additional or different integer execution units may be present inanother embodiment.

A memory execution (ME) scheduler 650 may schedule memory operations forexecution in an address generation unit (AGU) 652, which is also coupledto a TLB 654. As seen, these structures may couple to a data cache 660,which may be a L0 and/or L1 data cache that in turn couples toadditional levels of a cache memory hierarchy, including an L2 cachememory.

To provide support for out-of-order execution, an allocator/renamer 670may be provided, in addition to a reorder buffer 680, which isconfigured to reorder instructions executed out of order for retirementin order. Although shown with this particular pipeline architecture inthe illustration of FIG. 6, understand that many variations andalternatives are possible.

Note that in a processor having asymmetric cores, such as in accordancewith the micro-architectures of FIGS. 5 and 6, workloads may bedynamically swapped between the cores for power management reasons, asthese cores, although having different pipeline designs and depths, maybe of the same or related ISA. Such dynamic core swapping may beperformed in a manner transparent to a user application (and possiblykernel also).

Referring to FIG. 7, shown is a block diagram of a micro-architecture ofa processor core in accordance with yet another embodiment. Asillustrated in FIG. 7, a core 700 may include a multi-staged in-orderpipeline to execute at very low power consumption levels. As one suchexample, processor 700 may have a micro-architecture in accordance withan ARM Cortex A53 design available from ARM Holdings, LTD., Sunnyvale,Calif. In an implementation, an 8-stage pipeline may be provided that isconfigured to execute both 32-bit and 64-bit code. Core 700 includes afetch unit 710 that is configured to fetch instructions and provide themto a decode unit 715, which may decode the instructions, e.g.,macro-instructions of a given ISA such as an ARMv8 ISA. Note furtherthat a queue 730 may couple to decode unit 715 to store decodedinstructions. Decoded instructions are provided to an issue logic 725,where the decoded instructions may be issued to a given one of multipleexecution units.

With further reference to FIG. 7, issue logic 725 may issue instructionsto one of multiple execution units. In the embodiment shown, theseexecution units include an integer unit 735, a multiply unit 740, afloating point/vector unit 750, a dual issue unit 760, and a load/storeunit 770. The results of these different execution units may be providedto a writeback (WB) unit 780. Understand that while a single writebackunit is shown for ease of illustration, in some implementations separatewriteback units may be associated with each of the execution units.Furthermore, understand that while each of the units and logic shown inFIG. 7 is represented at a high level, a particular implementation mayinclude more or different structures. A processor designed using one ormore cores having a pipeline as in FIG. 7 may be implemented in manydifferent end products, extending from mobile devices to server systems.

Referring to FIG. 8, shown is a block diagram of a micro-architecture ofa processor core in accordance with a still further embodiment. Asillustrated in FIG. 8, a core 800 may include a multi-stage multi-issueout-of-order pipeline to execute at very high performance levels (whichmay occur at higher power consumption levels than core 700 of FIG. 7).As one such example, processor 800 may have a microarchitecture inaccordance with an ARM Cortex A57 design. In an implementation, a 15 (orgreater)-stage pipeline may be provided that is configured to executeboth 32-bit and 64-bit code. In addition, the pipeline may provide for 3(or greater)-wide and 3 (or greater)-issue operation. Core 800 includesa fetch unit 810 that is configured to fetch instructions and providethem to a decoder/renamer/dispatcher unit 815 coupled to a cache 820.Unit 815 may decode the instructions, e.g., macro-instructions of anARMv8 instruction set architecture, rename register references withinthe instructions, and dispatch the instructions (eventually) to aselected execution unit. Decoded instructions may be stored in a queue825. Note that while a single queue structure is shown for ease ofillustration in FIG. 8, understand that separate queues may be providedfor each of the multiple different types of execution units.

Also shown in FIG. 8 is an issue logic 830 from which decodedinstructions stored in queue 825 may be issued to a selected executionunit. Issue logic 830 also may be implemented in a particular embodimentwith a separate issue logic for each of the multiple different types ofexecution units to which issue logic 830 couples.

Decoded instructions may be issued to a given one of multiple executionunits. In the embodiment shown, these execution units include one ormore integer units 835, a multiply unit 840, a floating point/vectorunit 850, a branch unit 860, and a load/store unit 870. In anembodiment, floating point/vector unit 850 may be configured to handleSIMD or vector data of 128 or 256 bits. Still further, floatingpoint/vector execution unit 850 may perform IEEE-754 double precisionfloating-point operations. The results of these different executionunits may be provided to a writeback unit 880. Note that in someimplementations separate writeback units may be associated with each ofthe execution units. Furthermore, understand that while each of theunits and logic shown in FIG. 8 is represented at a high level, aparticular implementation may include more or different structures.

Note that in a processor having asymmetric cores, such as in accordancewith the micro-architectures of FIGS. 7 and 8, workloads may bedynamically swapped for power management reasons, as these cores,although having different pipeline designs and depths, may be of thesame or related ISA. Such dynamic core swapping may be performed in amanner transparent to a user application (and possibly kernel also).

A processor designed using one or more cores having pipelines as in anyone or more of FIGS. 5-8 may be implemented in many different endproducts, extending from mobile devices to server systems. Referring nowto FIG. 9, shown is a block diagram of a processor in accordance withanother embodiment of the present invention. In the embodiment of FIG.9, processor 900 may be a SoC including multiple domains, each of whichmay be controlled to operate at an independent operating voltage andoperating frequency. As a specific illustrative example, processor 900may be an Intel® Architecture Core™-based processor such as an i3, i5,i7 or another such processor available from Intel Corporation. However,other low power processors such as available from Advanced MicroDevices, Inc. (AMD) of Sunnyvale, Calif., an ARM-based design from ARMHoldings, Ltd. or licensee thereof or a MIPS-based design from MIPSTechnologies, Inc. of Sunnyvale, Calif., or their licensees or adoptersmay instead be present in other embodiments such as an Apple A7processor, a Qualcomm Snapdragon processor, or Texas Instruments OMAPprocessor. Such SoC may be used in a low power system such as asmartphone, tablet computer, phablet computer, Ultrabook™ computer orother portable computing device, which may incorporate a heterogeneoussystem architecture having a heterogeneous system architecture-basedprocessor design.

In the high level view shown in FIG. 9, processor 900 includes aplurality of core units 910 a-910 n. Each core unit may include one ormore processor cores, one or more cache memories and other circuitry.Each core unit 910 may support one or more instruction sets (e.g., anx86 instruction set (with some extensions that have been added withnewer versions); a MIPS instruction set; an ARM instruction set (withoptional additional extensions such as NEON)) or other instruction setor combinations thereof. Note that some of the core units may beheterogeneous resources (e.g., of a different design). In addition, eachsuch core may be coupled to a cache memory (not shown) which in anembodiment may be a shared level two (L2) cache memory. A non-volatilestorage 930 may be used to store various program and other data. Forexample, this storage may be used to store at least portions ofmicrocode, boot information such as a BIOS, other system software or soforth.

Each core unit 910 may also include an interface such as a bus interfaceunit to enable interconnection to additional circuitry of the processor.In an embodiment, each core unit 910 couples to a coherent fabric thatmay act as a primary cache coherent on-die interconnect that in turncouples to a memory controller 935. In turn, memory controller 935controls communications with a memory such as a DRAM (not shown for easeof illustration in FIG. 9).

In addition to core units, additional processing engines are presentwithin the processor, including at least one graphics unit 920 which mayinclude one or more graphics processing units (GPUs) to perform graphicsprocessing as well as to possibly execute general purpose operations onthe graphics processor (so-called GPGPU operation). In addition, atleast one image signal processor 925 may be present. Signal processor925 may be configured to process incoming image data received from oneor more capture devices, either internal to the SoC or off-chip.

Other accelerators also may be present. In the illustration of FIG. 9, avideo coder 950 may perform coding operations including encoding anddecoding for video information, e.g., providing hardware accelerationsupport for high definition video content. A display controller 955further may be provided to accelerate display operations includingproviding support for internal and external displays of a system. Inaddition, a security processor 945 may be present to perform securityoperations such as secure boot operations, various cryptographyoperations and so forth.

Each of the units may have its power consumption controlled via a powermanager 940, which may include control logic to perform the variouspower management techniques described herein.

In some embodiments, SoC 900 may further include a non-coherent fabriccoupled to the coherent fabric to which various peripheral devices maycouple. One or more interfaces 960 a-960 d enable communication with oneor more off-chip devices. Such communications may be via a variety ofcommunication protocols such as PCIe™, GPIO, USB, I²C, UART, MIPI, SDIO,DDR, SPI, HDMI, among other types of communication protocols. Althoughshown at this high level in the embodiment of FIG. 9, understand thescope of the present invention is not limited in this regard.

Referring now to FIG. 10, shown is a block diagram of a representativeSoC. In the embodiment shown, SoC 1000 may be a multi-core SoCconfigured for low power operation to be optimized for incorporationinto a smartphone or other low power device such as a tablet computer orother portable computing device. As an example, SoC 1000 may beimplemented using asymmetric or different types of cores, such ascombinations of higher power and/or low power cores, e.g., out-of-ordercores and in-order cores. In different embodiments, these cores may bebased on an Intel® Architecture™ core design or an ARM architecturedesign. In yet other embodiments, a mix of Intel and ARM cores may beimplemented in a given SoC.

As seen in FIG. 10, SoC 1000 includes a first core domain 1010 having aplurality of first cores 1012 a-1012 d. In an example, these cores maybe low power cores such as in-order cores. In one embodiment these firstcores may be implemented as ARM Cortex A53 cores. In turn, these corescouple to a cache memory 1015 of core domain 1010. In addition, SoC 1000includes a second core domain 1020. In the illustration of FIG. 10,second core domain 1020 has a plurality of second cores 1022 a-1022 d.In an example, these cores may be higher power-consuming cores thanfirst cores 1012. In an embodiment, the second cores may be out-of-ordercores, which may be implemented as ARM Cortex A57 cores. In turn, thesecores couple to a cache memory 1025 of core domain 1020. Note that whilethe example shown in FIG. 10 includes 4 cores in each domain, understandthat more or fewer cores may be present in a given domain in otherexamples.

With further reference to FIG. 10, a graphics domain 1030 also isprovided, which may include one or more graphics processing units (GPUs)configured to independently execute graphics workloads, e.g., providedby one or more cores of core domains 1010 and 1020. As an example, GPUdomain 1030 may be used to provide display support for a variety ofscreen sizes, in addition to providing graphics and display renderingoperations.

As seen, the various domains couple to a coherent interconnect 1040,which in an embodiment may be a cache coherent interconnect fabric thatin turn couples to an integrated memory controller 1050. Coherentinterconnect 1040 may include a shared cache memory, such as an L3cache, in some examples. In an embodiment, memory controller 1050 may bea direct memory controller to provide for multiple channels ofcommunication with an off-chip memory, such as multiple channels of aDRAM (not shown for ease of illustration in FIG. 10).

In different examples, the number of the core domains may vary. Forexample, for a low power SoC suitable for incorporation into a mobilecomputing device, a limited number of core domains such as shown in FIG.10 may be present. Still further, in such low power SoCs, core domain1020 including higher power cores may have fewer numbers of such cores.For example, in one implementation two cores 1022 may be provided toenable operation at reduced power consumption levels. In addition, thedifferent core domains may also be coupled to an interrupt controller toenable dynamic swapping of workloads between the different domains.

In yet other embodiments, a greater number of core domains, as well asadditional optional IP logic may be present, in that an SoC can bescaled to higher performance (and power) levels for incorporation intoother computing devices, such as desktops, servers, high performancecomputing systems, base stations forth. As one such example, 4 coredomains each having a given number of out-of-order cores may beprovided. Still further, in addition to optional GPU support (which asan example may take the form of a GPGPU), one or more accelerators toprovide optimized hardware support for particular functions (e.g. webserving, network processing, switching or so forth) also may beprovided. In addition, an input/output interface may be present tocouple such accelerators to off-chip components.

Referring now to FIG. 11, shown is a block diagram of another exampleSoC. In the embodiment of FIG. 11, SoC 1100 may include variouscircuitry to enable high performance for multimedia applications,communications and other functions. As such, SoC 1100 is suitable forincorporation into a wide variety of portable and other devices, such assmartphones, tablet computers, smart TVs and so forth. In the exampleshown, SoC 1100 includes a central processor unit (CPU) domain 1110. Inan embodiment, a plurality of individual processor cores may be presentin CPU domain 1110. As one example, CPU domain 1110 may be a quad coreprocessor having 4 multithreaded cores. Such processors may behomogeneous or heterogeneous processors, e.g., a mix of low power andhigh power processor cores.

In turn, a GPU domain 1120 is provided to perform advanced graphicsprocessing in one or more GPUs to handle graphics and compute APIs. ADSP unit 1130 may provide one or more low power DSPs for handlinglow-power multimedia applications such as music playback, audio/videoand so forth, in addition to advanced calculations that may occur duringexecution of multimedia instructions. In turn, a communication unit 1140may include various components to provide connectivity via variouswireless protocols, such as cellular communications (including 3G/4GLTE), wireless local area protocols such as Bluetooth™ IEEE 802.11, andso forth.

Still further, a multimedia processor 1150 may be used to performcapture and playback of high definition video and audio content,including processing of user gestures. A sensor unit 1160 may include aplurality of sensors and/or a sensor controller to interface to variousoff-chip sensors present in a given platform. An image signal processor1170 may be provided with one or more separate ISPs to perform imageprocessing with regard to captured content from one or more cameras of aplatform, including still and video cameras.

A display processor 1180 may provide support for connection to a highdefinition display of a given pixel density, including the ability towirelessly communicate content for playback on such display. Stillfurther, a location unit 1190 may include a GPS receiver with supportfor multiple GPS constellations to provide applications highly accuratepositioning information obtained using as such GPS receiver. Understandthat while shown with this particular set of components in the exampleof FIG. 11, many variations and alternatives are possible.

Referring now to FIG. 12, shown is a block diagram of an example systemwith which embodiments can be used. As seen, system 1200 may be asmartphone or other wireless communicator. A baseband processor 1205 isconfigured to perform various signal processing with regard tocommunication signals to be transmitted from or received by the system.In turn, baseband processor 1205 is coupled to an application processor1210, which may be a main CPU of the system to execute an OS and othersystem software, in addition to user applications such as manywell-known social media and multimedia apps. Application processor 1210may further be configured to perform a variety of other computingoperations for the device.

In turn, application processor 1210 can couple to a userinterface/display 1220, e.g., a touch screen display. In addition,application processor 1210 may couple to a memory system including anon-volatile memory, namely a flash memory 1230 and a system memory,namely a dynamic random access memory (DRAM) 1235. As further seen,application processor 1210 further couples to a capture device 1240 suchas one or more image capture devices that can record video and/or stillimages.

Still referring to FIG. 12, a universal integrated circuit card (UICC)1240 comprising a subscriber identity module and possibly a securestorage and cryptoprocessor is also coupled to application processor1210. System 1200 may further include a security processor 1250 that maycouple to application processor 1210. A plurality of sensors 1225 maycouple to application processor 1210 to enable input of a variety ofsensed information such as accelerometer and other environmentalinformation. An audio output device 1295 may provide an interface tooutput sound, e.g., in the form of voice communications, played orstreaming audio data and so forth.

As further illustrated, a near field communication (NFC) contactlessinterface 1260 is provided that communicates in a NFC near field via anNFC antenna 1265. While separate antennae are shown in FIG. 12,understand that in some implementations one antenna or a different setof antennae may be provided to enable various wireless functionality.

A power management integrated circuit (PMIC) 1215 couples to applicationprocessor 1210 to perform platform level power management. To this end,PMIC 1215 may issue power management requests to application processor1210 to enter certain low power states as desired. Furthermore, based onplatform constraints, PMIC 1215 may also control the power level ofother components of system 1200.

To enable communications to be transmitted and received, variouscircuitry may be coupled between baseband processor 1205 and an antenna1290. Specifically, a radio frequency (RF) transceiver 1270 and awireless local area network (WLAN) transceiver 1275 may be present. Ingeneral, RF transceiver 1270 may be used to receive and transmitwireless data and calls according to a given wireless communicationprotocol such as 3G or 4G wireless communication protocol such as inaccordance with a code division multiple access (CDMA), global systemfor mobile communication (GSM), long term evolution (LTE) or otherprotocol. In addition a GPS sensor 1280 may be present. Other wirelesscommunications such as receipt or transmission of radio signals, e.g.,AM/FM and other signals may also be provided. In addition, via WLANtransceiver 1275, local wireless communications can also be realized.

Referring now to FIG. 13, shown is a block diagram of another examplesystem with which embodiments may be used. In the illustration of FIG.13, system 1300 may be mobile low-power system such as a tabletcomputer, 2:1 tablet, phablet or other convertible or standalone tabletsystem. As illustrated, a SoC 1310 is present and may be configured tooperate as an application processor for the device.

A variety of devices may couple to SoC 1310. In the illustration shown,a memory subsystem includes a flash memory 1340 and a DRAM 1345 coupledto SoC 1310. In addition, a touch panel 1320 is coupled to the SoC 1310to provide display capability and user input via touch, includingprovision of a virtual keyboard on a display of touch panel 1320. Toprovide wired network connectivity, SoC 1310 couples to an Ethernetinterface 1330. A peripheral hub 1325 is coupled to SoC 1310 to enableinterfacing with various peripheral devices, such as may be coupled tosystem 1300 by any of various ports or other connectors.

In addition to internal power management circuitry and functionalitywithin SoC 1310, a PMIC 1380 is coupled to SoC 1310 to provideplatform-based power management, e.g., based on whether the system ispowered by a battery 1390 or AC power via an AC adapter 1395. Inaddition to this power source-based power management, PMIC 1380 mayfurther perform platform power management activities based onenvironmental and usage conditions. Still further, PMIC 1380 maycommunicate control and status information to SoC 1310 to cause variouspower management actions within SoC 1310.

Still referring to FIG. 13, to provide for wireless capabilities, a WLANunit 1350 is coupled to SoC 1310 and in turn to an antenna 1355. Invarious implementations, WLAN unit 1350 may provide for communicationaccording to one or more wireless protocols.

As further illustrated, a plurality of sensors 1360 may couple to SoC1310. These sensors may include various accelerometer, environmental andother sensors, including user gesture sensors. Finally, an audio codec1365 is coupled to SoC 1310 to provide an interface to an audio outputdevice 1370. Of course understand that while shown with this particularimplementation in FIG. 13, many variations and alternatives arepossible.

Referring now to FIG. 14, shown is a block diagram of a representativecomputer system such as notebook, Ultrabook™ or other small form factorsystem. A processor 1410, in one embodiment, includes a microprocessor,multi-core processor, multithreaded processor, an ultra low voltageprocessor, an embedded processor, or other known processing element. Inthe illustrated implementation, processor 1410 acts as a main processingunit and central hub for communication with many of the variouscomponents of the system 1400, and may include power managementcircuitry as described herein. As one example, processor 1410 isimplemented as a SoC.

Processor 1410, in one embodiment, communicates with a system memory1415. As an illustrative example, the system memory 1415 is implementedvia multiple memory devices or modules to provide for a given amount ofsystem memory.

To provide for persistent storage of information such as data,applications, one or more operating systems and so forth, a mass storage1420 may also couple to processor 1410. In various embodiments, toenable a thinner and lighter system design as well as to improve systemresponsiveness, this mass storage may be implemented via a SSD or themass storage may primarily be implemented using a hard disk drive (HDD)with a smaller amount of SSD storage to act as a SSD cache to enablenon-volatile storage of context state and other such information duringpower down events so that a fast power up can occur on re-initiation ofsystem activities. Also shown in FIG. 14, a flash device 1422 may becoupled to processor 1410, e.g., via a serial peripheral interface(SPI). This flash device may provide for non-volatile storage of systemsoftware, including a basic input/output software (BIOS) as well asother firmware of the system.

Various input/output (I/O) devices may be present within system 1400.Specifically shown in the embodiment of FIG. 14 is a display 1424 whichmay be a high definition LCD or LED panel that further provides for atouch screen 1425. In one embodiment, display 1424 may be coupled toprocessor 1410 via a display interconnect that can be implemented as ahigh performance graphics interconnect. Touch screen 1425 may be coupledto processor 1410 via another interconnect, which in an embodiment canbe an I²C interconnect. As further shown in FIG. 14, in addition totouch screen 1425, user input by way of touch can also occur via a touchpad 1430 which may be configured within the chassis and may also becoupled to the same I²C interconnect as touch screen 1425.

For perceptual computing and other purposes, various sensors may bepresent within the system and may be coupled to processor 1410 indifferent manners. Certain inertial and environmental sensors may coupleto processor 1410 through a sensor hub 1440, e.g., via an I²Cinterconnect. In the embodiment shown in FIG. 14, these sensors mayinclude an accelerometer 1441, an ambient light sensor (ALS) 1442, acompass 1443 and a gyroscope 1444. Other environmental sensors mayinclude one or more thermal sensors 1446 which in some embodimentscouple to processor 1410 via a system management bus (SMBus) bus.

Also seen in FIG. 14, various peripheral devices may couple to processor1410 via a low pin count (LPC) interconnect. In the embodiment shown,various components can be coupled through an embedded controller 1435.Such components can include a keyboard 1436 (e.g., coupled via a PS2interface), a fan 1437, and a thermal sensor 1439. In some embodiments,touch pad 1430 may also couple to EC 1435 via a PS2 interface. Inaddition, a security processor such as a trusted platform module (TPM)1438 may also couple to processor 1410 via this LPC interconnect.

System 1400 can communicate with external devices in a variety ofmanners, including wirelessly. In the embodiment shown in FIG. 14,various wireless modules, each of which can correspond to a radioconfigured for a particular wireless communication protocol, arepresent. One manner for wireless communication in a short range such asa near field may be via a NFC unit 1445 which may communicate, in oneembodiment with processor 1410 via an SMBus. Note that via this NFC unit1445, devices in close proximity to each other can communicate.

As further seen in FIG. 14, additional wireless units can include othershort range wireless engines including a WLAN unit 1450 and a Bluetooth™unit 1452. Using WLAN unit 1450, Wi-Fi™ communications can be realized,while via Bluetooth™ unit 1452, short range Bluetooth™ communicationscan occur. These units may communicate with processor 1410 via a givenlink.

In addition, wireless wide area communications, e.g., according to acellular or other wireless wide area protocol, can occur via a WWAN unit1456 which in turn may couple to a subscriber identity module (SIM)1457. In addition, to enable receipt and use of location information, aGPS module 1455 may also be present. Note that in the embodiment shownin FIG. 14, WWAN unit 1456 and an integrated capture device such as acamera module 1454 may communicate via a given link.

To provide for audio inputs and outputs, an audio processor can beimplemented via a digital signal processor (DSP) 1460, which may coupleto processor 1410 via a high definition audio (HDA) link. Similarly, DSP1460 may communicate with an integrated coder/decoder (CODEC) andamplifier 1462 that in turn may couple to output speakers 1463 which maybe implemented within the chassis. Similarly, amplifier and CODEC 1462can be coupled to receive audio inputs from a microphone 1465 which inan embodiment can be implemented via dual array microphones (such as adigital microphone array) to provide for high quality audio inputs toenable voice-activated control of various operations within the system.Note also that audio outputs can be provided from amplifier/CODEC 1462to a headphone jack 1464. Although shown with these particularcomponents in the embodiment of FIG. 14, understand the scope of thepresent invention is not limited in this regard.

Embodiments may be implemented in many different system types. Referringnow to FIG. 15, shown is a block diagram of a system in accordance withan embodiment of the present invention. As shown in FIG. 15,multiprocessor system 1500 is a point-to-point interconnect system, andincludes a first processor 1570 and a second processor 1580 coupled viaa point-to-point interconnect 1550. As shown in FIG. 15, each ofprocessors 1570 and 1580 may be multicore processors, including firstand second processor cores (i.e., processor cores 1574 a and 1574 b andprocessor cores 1584 a and 1584 b), although potentially many more coresmay be present in the processors. Each of the processors can include aPCU or other power management logic to perform processor-based powermanagement as described herein.

Still referring to FIG. 15, first processor 1570 further includes amemory controller hub (MCH) 1572 and point-to-point (P-P) interfaces1576 and 1578. Similarly, second processor 1580 includes a MCH 1582 andP-P interfaces 1586 and 1588. As shown in FIG. 15, MCH's 1572 and 1582couple the processors to respective memories, namely a memory 1532 and amemory 1534, which may be portions of system memory (e.g., DRAM) locallyattached to the respective processors. First processor 1570 and secondprocessor 1580 may be coupled to a chipset 1590 via P-P interconnects1562 and 1564, respectively. As shown in FIG. 15, chipset 1590 includesP-P interfaces 1594 and 1598.

Furthermore, chipset 1590 includes an interface 1592 to couple chipset1590 with a high performance graphics engine 1538, by a P-P interconnect1539. In turn, chipset 1590 may be coupled to a first bus 1516 via aninterface 1596. As shown in FIG. 15, various input/output (I/O) devices1514 may be coupled to first bus 1516, along with a bus bridge 1518which couples first bus 1516 to a second bus 1520. Various devices maybe coupled to second bus 1520 including, for example, a keyboard/mouse1522, communication devices 1526 and a data storage unit 1528 such as adisk drive or other mass storage device which may include code 1530, inone embodiment. Further, an audio I/O 1524 may be coupled to second bus1520. Embodiments can be incorporated into other types of systemsincluding mobile devices such as a smart cellular telephone, tabletcomputer, netbook, Ultrabook™, or so forth.

One or more aspects of at least one embodiment may be implemented byrepresentative code stored on a machine-readable medium which representsand/or defines logic within an integrated circuit such as a processor.For example, the machine-readable medium may include instructions whichrepresent various logic within the processor. When read by a machine,the instructions may cause the machine to fabricate the logic to performthe techniques described herein. Such representations, known as “IPcores,” are reusable units of logic for an integrated circuit that maybe stored on a tangible, machine-readable medium as a hardware modelthat describes the structure of the integrated circuit. The hardwaremodel may be supplied to various customers or manufacturing facilities,which load the hardware model on fabrication machines that manufacturethe integrated circuit. The integrated circuit may be fabricated suchthat the circuit performs operations described in association with anyof the embodiments described herein.

FIG. 16 is a block diagram illustrating an IP core development system1600 that may be used to manufacture an integrated circuit to performoperations according to an embodiment. The IP core development system1600 may be used to generate modular, reusable designs that can beincorporated into a larger design or used to construct an entireintegrated circuit (e.g., an SoC integrated circuit). A design facility1630 can generate a software simulation 1610 of an IP core design in ahigh level programming language (e.g., C/C++). The software simulation1610 can be used to design, test, and verify the behavior of the IPcore. A register transfer level (RTL) design can then be created orsynthesized from the simulation model. The RTL design 1615 is anabstraction of the behavior of the integrated circuit that models theflow of digital signals between hardware registers, including theassociated logic performed using the modeled digital signals. Inaddition to an RTL design 1615, lower-level designs at the logic levelor transistor level may also be created, designed, or synthesized. Thus,the particular details of the initial design and simulation may vary.

The RTL design 1615 or equivalent may be further synthesized by thedesign facility into a hardware model 1620, which may be in a hardwaredescription language (HDL), or some other representation of physicaldesign data. The HDL may be further simulated or tested to verify the IPcore design. The IP core design can be stored for delivery to a thirdparty fabrication facility 1665 using non-volatile memory 1640 (e.g.,hard disk, flash memory, or any non-volatile storage medium).Alternately, the IP core design may be transmitted (e.g., via theInternet) over a wired connection 1650 or wireless connection 1660. Thefabrication facility 1665 may then fabricate an integrated circuit thatis based at least in part on the IP core design. The fabricatedintegrated circuit can be configured to perform operations in accordancewith at least one embodiment described herein.

Referring now to FIG. 17, shown is a block diagram of a system 1700 forprefetch throttling in accordance with one or more embodiments. In someembodiments, the system 1700 may be all or a portion of an electronicdevice or component. For example, the system 1700 may be a cellulartelephone, a computer, a server, a network device, a system on a chip(SoC), a controller, a wireless transceiver, a power supply unit, etc.Furthermore, in some embodiments, the system 1700 may be any grouping ofrelated or interconnected devices, such as a datacenter, a computingcluster, etc.

As shown in FIG. 17, the system 1700 may include a processor 1710operatively coupled to system memory 1705. Further, although not shownin FIG. 17, the system 1700 may include other components. In one or moreembodiments, the system memory 1705 can be implemented with any type(s)of computer memory (e.g., dynamic random access memory (DRAM), staticrandom-access memory (SRAM), non-volatile memory (NVM), a combination ofDRAM and NVM, etc.).

The processor 1710 may be a general purpose hardware processing device(e.g., a central processing unit (CPU), a System on a Chip (SoC), and soforth). As shown, the processor 1710 can include any number ofprocessing cores 1715A-1715N (also referred to collectively as cores1715). Each core 1715 may be a general purpose processing core. In oneor more embodiments, each core 1715 may include a prefetch circuit 1720and a prefetch history array 1725. The prefetch circuit 1720 and/or theprefetch history array 1725 may be implemented in circuitry and/ormicro-architecture of the core 1715 and/or the processor 1710. In someembodiments, the prefetch circuit 1720 may include a short streamcounter 1722. As described below with reference to FIG. 20, the shortstream counter 1722 may be used to determine whether to throttle theprefetch circuit 1720.

In some embodiments, the prefetch circuit 1720 may initiate, manage,and/or execute prefetch requests in the respective core 1715. Forexample, the prefetch circuit 1720 may analyze memory access requests todetermine a data usage pattern in the core 1715. The prefetch circuit1720 may use the usage pattern to predict data that will be needed bythe core 1715 in a given time window. The prefetch circuit 1720 may thenautomatically generate a prefetch request for the predicted data.Further, in some embodiments, the prefetch circuit 1720 may execute theprefetch request to read the predicted data from memory, and may storethe read data in a cache or storage of the core 1715.

In some embodiments, the prefetch history array 1725 may storehistorical information about data used by the processing core 1715. Theprefetch circuit 1720 may interact with the prefetch history array 1725to try to predict the data that will be required in the near future. Insome embodiments, the prefetch circuit 1720 may try to determine thenext data load from memory using a constant stride calculation, or afixed distance between subsequent accesses to the same memory area. Theprefetch circuit 1720 may then generate a prefetch request with thepredicted address.

Referring now to FIG. 18, shown is an example of the prefetch historyarray 1800 in accordance with some embodiments. The prefetch historyarray 1800 may correspond generally to an example embodiment of theprefetch history array 1725 (shown in FIG. 17). As shown in FIG. 18, theprefetch history array 1800 may include a plurality of entries. In oneor more embodiments, each entry of the prefetch history array 1800 mayinclude a plurality of fields. For example, each entry may some or allof an address field, a stride field, a state field, and/or a sublengthfield.

In one or more embodiments, the address field of an entry may store aunique address or tag associated with a load from memory. For example,in some embodiments, the address field of an entry may store theinstruction pointer address associated with a data load. In someembodiments, the entries of the prefetch history array 1800 may beindexed according to the address field. In some embodiments, the stridefield of an entry may store the stride or distance between subsequentaccesses to the entry address (i.e., the entry address identified by theaddress field).

In one or more embodiments, the state field of an entry may storeinformation related to a state or state machine associated with theentry address. For example, the state field may store an indication of astate (e.g., a bit indicator), a state machine data structure, a pointerto a state machine data structure, and so forth. In some embodiments,the sublength field of an entry may store a sublength value associatedwith the entry address. As used herein, the term “sublength value”refers to a numeric value that provides an indication of how frequentlya stride has been repeated during a recent series of loads. Examples ofa state machine and a sublength value are described further below withreference to FIG. 19. Further, in some embodiments, each entry of theprefetch history array 1800 may include other fields (e.g., thresholdvalues, maximum values, minimum values, etc.).

Referring now to FIG. 19, shown is an example state machine 1900 inaccordance with some embodiments. In one or more embodiments, the statemachine 1900 may be generated and/or maintained by the prefetch circuit1720 (shown in FIG. 17). Further, in some embodiments, informationrelated to the state machine 1900 (e.g., a state indication, a pointer,etc.) may be stored in each state field of the prefetch history array1800 (shown in FIG. 18). In some embodiments, the state machine 1900 maybe uniquely associated with particular entry or entry address.

As shown in FIG. 19, in some embodiments, the state machine 1900 mayinclude an initialization state 1910, a detection state 1920, a firststride state 1930, and a second stride state 1940. In one or moreembodiments, the state machine 1900 is uniquely associated with theentry address of the entry storing the state machine 1900. In someembodiments, the initialization state 1910 may be entered on start-up orreset of a processor. In response to a detection of a load associatedwith the entry address, the state machine 1900 may transition 1915 tothe detection state 1920.

While in the detection state 1920, each load may be evaluated to detecta stride. For example, in some embodiments, a stride may be detected ifthe same distance is used for a number of consecutive loads (e.g., twoloads, three loads, etc.). If no stride is detected, the state machine1900 may perform a return cycle 1922 to remain in the detection state1920. However, when a stride is detected, the state machine 1900 maytransition 1925 to the first stride state 1930, and the sublength valueassociated with the entry address may be set to an initial value (e.g.,a value of three). In some embodiments, the sublength value may bestored in the sublength field of an entry of the prefetch history array1800 (shown in FIG. 18). In some embodiments, the sublength value may beuniquely associated with the entry address.

While in the first stride state 1930, the subsequent loads are evaluatedto determine if the detected stride (i.e., the stride detected in thedetection state 1920) is repeated. Each instance of a repeated stridemay be referred to herein as a “stride match.” If the next load has astride match to the detected stride, the state machine 1900 may performa return cycle 1932 to remain in the first stride state 1930, and thesublength value may be incremented by a value of one. However, if thenext load does not have a stride match to the detected stride (i.e., theload occurs at a different distance than the detected stride), the statemachine 1900 may transition 1935 to the second stride state 1940, andthe sublength value may be set to a value of one.

While in the second stride state 1940, the next load is evaluated todetermine if the next load has a stride match to the detected stride(i.e., the stride detected in the detection state 1920). If the nextload does not have a stride match to the detected stride, the statemachine 1900 may transition 1946 back to the initialization state 1920,and the sublength value may be set to value of zero. Note that, in thissituation, the last two loads did not match the detected stride.However, if the next load has a stride match to the detected stride, thestate machine 1900 may transition 1943 back to the first stride state1930, and the sublength value may be set to value of two.

Note that, in the example of FIG. 19, the adjustments to the sublengthvalue are based on the number of stride matches to the detected stride.Thus, in some embodiments, a sublength value may provide an indicationof how frequently the detected stride is repeated during a recent seriesof loads.

In some embodiments, the sublength values included in a prefetch historyarray may be used to adjust the short stream counter 1722 (shown in FIG.17). For example, in some embodiments, the short stream counter 1722 maybe decremented when a sublength value exceeds a defined short streamthreshold. In another example, in some embodiments, the short streamcounter 1722 may be incremented when a sublength value does not exceedthe defined short stream threshold. In some embodiments, the shortstream counter 1722 may be a global counter based on all sublengthvalues of a prefetcher (e.g., corresponding to all entries of theprefetch history array 1725 shown in FIG. 17). Further, in someembodiments, the short stream counter 1722 may be used to determinewhether to throttle a level of prefetching. Some example processes usinga short stream counter for prefetch throttling are described below withreference to FIGS. 20-21.

Referring now to FIG. 20, shown is a flow diagram of a method 2000 forprefetch throttling in accordance with one or more embodiments. Invarious embodiments, the method 2000 may be performed by processinglogic that may include hardware (e.g., processing device, circuitry,dedicated logic, programmable logic, microcode, etc.), software (e.g.,instructions run on a processing device), or a combination thereof. Insome implementations, the method 2000 may be performed using one or morecomponents shown in FIGS. 17-19 (e.g., prefetch circuit 1720 and/orprefetch history array 1725). In firmware or software embodiments, themethod 2000 may be implemented by computer executed instructions storedin a non-transitory machine readable medium, such as an optical,semiconductor, or magnetic storage device. The machine readable mediummay store data, which if used by at least one machine, causes the atleast one machine to fabricate at least one integrated circuit toperform a method. For the sake of illustration, the actions involved inthe method 2000 may be described below with reference to FIGS. 17-19,which show examples in accordance with one or more embodiments. However,the scope of the various embodiments discussed herein is not limited inthis regard.

At block 2010, a load event in a processor may be detected. For example,referring to FIG. 17, the prefetch circuit 1720 may detect a load ofdata from system memory 1705 to processing core 1715A.

At block 2020, a sublength value may be determined for the load event(detected at box 2010). In some embodiments, the sublength value may bedetermined using a prefetch state machine. For example, referring toFIGS. 17-19, the prefetch circuit 1720 may update the state machine 1900based on the load event. The sublength value may be adjusted based ontransitions between the detection state 1920, the first stride state1930, and the second stride state 1940. In one or more embodiments, thesublength value may be stored in an entry of the prefetch history array1725. In some embodiments, the entry may be tagged with an addresscorresponding to the load (e.g., an instruction pointer address).

At diamond 2030, a determination may be made about whether the sublengthvalue (determined at box 2020) exceeds a short stream threshold. Forexample, referring to FIG. 17, the prefetch circuit 1720 may determinewhether the sublength value in an entry of the prefetch history array1725 exceeds a defined short stream threshold. In some embodiments, theshort stream threshold may be set by a configurable parameter of theprefetch circuit 1720.

If it is determined at diamond 2030 that the sublength value does notexceed the short stream threshold, then at diamond 2040, a determinationmay be made about whether a short stream counter is at a maximum allowedvalue. For example, referring to FIG. 17, the prefetch circuit 1720 maydetermine whether the short stream counter 1722 is saturated at amaximum allowed value. In some embodiments, the maximum allowed value ofthe short stream counter 1722 may be set by a configurable parameter ofthe prefetch circuit 1720. In some embodiments, the short stream counter1722 may be a global short stream counter (i.e., based on all sublengthvalues of the prefetch history array 1725).

If it is determined at diamond 2040 that the short stream counter is atthe maximum allowed value, then the method 2000 continues at block 2080.However, if it is determined at diamond 2040 that the short streamcounter is not at the maximum allowed value, then at block 2050, theshort stream counter is incremented. For example, referring to FIG. 17,the prefetch circuit 1720 may determine that the short stream counter1722 is not at a maximum allowed value, and in response may incrementthe short stream counter 1722 by one. After box 2050, the method 2000continues at block 2080.

Referring again to diamond 2030, if it is determined that the sublengthvalue exceeds the short stream threshold, then at diamond 2060, adetermination may be made about whether the short stream counter is at aminimum allowed value (e.g., zero). For example, referring to FIG. 17,the prefetch circuit 1720 may determine whether the short stream counter1722 is currently at a minimum allowed value of zero. In someembodiments, the minimum allowed value of the short stream counter 1722may be set by a configurable parameter of the prefetch circuit 1720.

If it is determined at diamond 2060 that the short stream counter is ata minimum allowed value, then the method 2000 continues at block 2080.However, if it is determined at diamond 2060 that the short streamcounter is not at a minimum allowed value, then at block 2070, the shortstream counter is decremented. For example, referring to FIG. 17, theprefetch circuit 1720 may determine that the short stream counter 1722is not at a minimum allowed value, and in response may decrement theshort stream counter 1722 by one. After box 2070, the method 2000continues at block 2080.

At box 2080, a level of prefetch throttling may be adjusted based on thevalue of the short stream counter. In some embodiments, the level ofprefetch throttling may be determined based on whether the short streamcounter has exceeded a throttling threshold. For example, referring toFIG. 17, the prefetch circuit 1720 may compare the value of the shortstream counter 1722 to a defined throttling threshold. In someembodiments, if the short stream counter 1722 exceeds the throttlingthreshold, the level of prefetch throttling may be increased. Further,in some embodiments, if the short stream counter 1722 does not exceedthe throttling threshold, the level of prefetch throttling may bereduced or stopped. In some embodiments, the throttling threshold may beset by a configurable parameter of the prefetch circuit 1720. Afterblock 2080, the method 2000 may return to block 2010 to wait for anotherdetection of a load event.

Referring now to FIG. 21, shown is a flow diagram of a method 2100 forprefetch throttling in accordance with one or more embodiments. Themethod 2100 may correspond generally to an example implementation of themethod 2000 shown in FIG. 20. In various embodiments, the method 2100may be performed by processing logic that may include hardware (e.g.,processing device, circuitry, dedicated logic, programmable logic,microcode, etc.), software (e.g., instructions run on a processingdevice), or a combination thereof. In some implementations, the method2100 may be performed using one or more components shown in FIGS. 17-19(e.g., prefetch circuit 1720 and/or prefetch history array 1725). Infirmware or software embodiments, the method 2100 may be implemented bycomputer executed instructions stored in a non-transitory machinereadable medium, such as an optical, semiconductor, or magnetic storagedevice. The machine readable medium may store data, which if used by atleast one machine, causes the at least one machine to fabricate at leastone integrated circuit to perform a method. For the sake ofillustration, the actions involved in the method 2100 may be describedbelow with reference to FIGS. 17-19, which show examples in accordancewith one or more embodiments. However, the scope of the variousembodiments discussed herein is not limited in this regard.

At block 2110, a prefetch history array may be maintained in aprocessor, with each entry of the prefetch history array comprising asublength value. For example, referring to FIGS. 17-18, the prefetchcircuit 1720 may maintain the prefetch history array 1800. Each entry ofthe prefetch history array 1800 includes a sublength field to store asublength value.

At block 2120, for each entry of the prefetch history array, thesublength value may be adjusted based on stride matches. In someembodiments, the sublength value may be adjusted using a prefetch statemachine. For example, referring to FIGS. 17-19, the prefetch circuit1720 may update the state machine 1900 of each entry based on stridematches in loads associated with the entry. Further, a sublength valuemay be adjusted based on the transitions in the state machine 1900.

At block 2130, a short stream counter may be adjusted based on thesublength values of the entries in the prefetch history array. Forexample, referring to FIG. 17, the prefetch circuit 1720 may evaluateeach sublength value in the prefetch history array 1725. In someembodiments, the prefetch circuit 1720 may increment or decrement theshort stream counter 1722 based on whether each sublength valuesatisfies a short stream threshold. For example, the prefetch circuit1720 may decrement the short stream counter 1722 in response to adetermination that a sublength value exceeds the short stream threshold.In another example, the prefetch circuit 1720 may increment the shortstream counter 1722 in response to a determination that a sublengthvalue does not exceed the short stream threshold. In some embodiments,the short stream counter 1722 may be a global short stream counter(i.e., based on all sublength values in the prefetch history array1725).

At block 2140, it may be determined whether the short stream counter hasexceeded a throttling threshold. At block 2150, a prefetch level may bethrottled in response to a determination that the short stream counterhas exceeded the throttling threshold. For example, referring to FIG.17, the prefetch circuit 1720 may determine that the value of the shortstream counter 1722 exceeds a throttling threshold. In response to thisdetermination, the prefetch circuit 1720 may increase a level ofprefetch throttling, thus reducing or stopping the prefetching performedby the prefetch circuit. In some embodiments, the level of prefetchthrottling corresponds to a number of levels (e.g., a number of programinstructions or loops) that are being prefetched ahead. After block2150, the method 2100 is completed.

Note that the examples shown in FIGS. 1-21 are provided for the sake ofillustration, and are not intended to limit any embodiments. Forexample, while FIGS. 18-21 show embodiments in which sublength valuesare stored in each entry of the prefetch history array 1725, and theshort stream counter 1722 is adjusted based on these stored sublengthvalues, other embodiments are possible. It is contemplated that, in someembodiments, the short stream counter 1722 may be incremented when astate machine 1900 is in the first stride state 1930, and may bedecremented when the state machine 1900 is not in the first stride state1930. Accordingly, in such embodiments, there is no need to store thesublength values in the prefetch history array 1725, and thus memory useand processing capacity may be reduced.

Note also that, while embodiments may be shown in simplified form forthe sake of clarity, embodiments may include any number and/orarrangement of processors, cores, and/or additional components (e.g.,buses, storage media, connectors, power components, buffers, interfaces,etc.). For example, it is contemplated that the prefetch circuit 1720and the prefetch history array 1725 may be located in a portion of theprocessor 170 that is external to the processing cores 1715 (e.g., anuncore region). Further, it is contemplated that some embodiments mayinclude any number of components in addition to those shown, and thatdifferent arrangement of the components shown may occur in certainimplementations. Furthermore, it is contemplated that specifics in theexamples shown in FIGS. 1-21 may be used anywhere in one or moreembodiments. For example, the components and/or functions discussedabove with respect to FIGS. 17-21 may be implemented in any of thesystems and/or components discussed above with respect to FIGS. 1-16.

The following clauses and/or examples pertain to further embodiments.

In one example, a processor for prefetch throttling includes a prefetchhistory array and a prefetch circuit. The prefetch history arraycomprises a plurality of entries corresponding to prefetch addresses,each entry of the plurality of entries comprising a sublength valueassociated with a frequency that a stride is repeated. The prefetchcircuit is to: for each entry of the plurality of entries, adjust thesublength value based on stride matches for an address of the entry;adjust a short stream counter based on the sublength values of theplurality of entries in the prefetch history array; determine whetherthe short stream counter has exceeded a throttling threshold; and inresponse to a determination that the short stream counter has exceededthe throttling threshold, throttle a prefetch level of the prefetchcircuit.

In an example, the prefetch circuit is further to, in response to adetermination that the short stream counter has not exceeded thethrottling threshold, reduce throttling of the prefetch level of theprefetch circuit.

In an example, the prefetch circuit is further to, for each entry of theplurality of entries, decrement the short stream counter in response toa determination that the sublength value has exceeded a short streamthreshold.

In an example, the prefetch circuit is further to, for each entry of theplurality of entries, increment the short stream counter in response toa determination that the sublength value has not exceeded the shortstream threshold.

In an example, each entry of the plurality of entries comprisesinformation related to a state machine including an initializationstate, a detection state, a first stride state, and a second stridestate. In an example, each entry of the plurality of entries furthercomprises an instruction pointer tag and a stride value. In an example,the prefetch circuit is further to, for each entry of the plurality ofentries: at a first point in time, in response to a detection of astride match when the state machine is in the detection state,transition the state machine to the first stride state and set thesublength value to an initial value; and at a second point in time, inresponse to a detection of a stride match when the state machine is inthe first stride state, increment the sublength value by one. In anexample, the prefetch circuit is further to, for each entry of theplurality of entries: at a third point in time, in response to adetection of a stride mismatch when the state machine is in the firststride state, transition the state machine to the second stride stateand set the sublength value to a value of one; at a fourth point intime, in response to a detection of a stride match when the statemachine is in the second stride state, transition the state machine tothe first stride state and set the sublength value to a value of two;and at a fifth point in time, in response to a detection of a stridemismatch when the state machine is in the second stride state,transition the state machine to the detection state and set thesublength value to a value of zero.

In one example, a method for prefetch throttling comprises: maintaining,by a prefetch circuit of a processor, a prefetch history arraycomprising a plurality of entries, each entry comprising a sublengthvalue associated with a frequency that a stride is repeated; for eachentry of the plurality of entries, the prefetch circuit adjusting thesublength value based on whether loads associated with the entry havestride matches; for each sublength value in the plurality of entries,the prefetch circuit adjusting a short stream counter based on whetherthe sublength value has exceeded a short stream threshold; and adjustinga prefetch level of the prefetch circuit based on whether the shortstream counter has exceeded a throttling threshold.

In an example, the method further comprises: determining that thesublength value has exceeded the short stream threshold; and in responseto determining that the sublength value has exceeded the short streamthreshold, decrementing the short stream counter.

In an example, the method further comprises: determining that thesublength value has not exceeded the short stream threshold; and inresponse to determining that the sublength value has not exceeded theshort stream threshold, incrementing the short stream counter.

In an example, the method further comprises: determining that the shortstream counter has exceeded the throttling threshold; and in response todetermining that the short stream counter has exceeded the throttlingthreshold, increasing throttling of the prefetch level of the prefetchcircuit.

In an example, the method further comprises: determining that the shortstream counter has not exceeded the throttling threshold; and inresponse to determining that the short stream counter has not exceededthe throttling threshold, decreasing throttling of the prefetch level ofthe prefetch circuit.

In an example, maintaining the prefetch history array further comprises,for each entry of the plurality of entries: maintaining a state machinecomprising an initialization state, a detection state, a first stridestate, and a second stride state; transitioning the state machine basedon stride matches; and adjusting the sublength value based ontransitions in the state machine.

In one example, a machine readable medium has stored thereon data, whichif used by at least one machine, causes the at least one machine tofabricate at least one integrated circuit to perform a method accordingto any one of the above examples.

In one example, an apparatus for processing instructions, is configuredto perform the method of any one of the above examples.

In one example, a system for prefetch throttling comprises a processorincluding a prefetch circuit, and an external memory coupled to theprocessor. The prefetch circuit is to: maintain a prefetch history arraycomprising a plurality of entries, each entry comprising a sublengthvalue associated with a frequency that a stride is repeated; adjust thesublength values of the plurality of entries based on stride matches;adjust a short stream counter based on the sublength values of theplurality of entries in the prefetch history array; and adjust aprefetch level of the prefetch circuit based on a comparison of theshort stream counter to a throttling threshold; and

In an example, the prefetch circuit is further to increase throttling ofthe prefetch level of the prefetch circuit in response to adetermination that the short stream counter has exceeded the throttlingthreshold.

In an example, the prefetch circuit is further to decrease throttling ofthe prefetch level of the prefetch circuit in response to adetermination that the short stream counter has not exceeded thethrottling threshold.

In an example, the prefetch circuit is further to decrement the shortstream counter in response to a determination that the sublength valuehas exceeded the short stream threshold.

In an example, the prefetch circuit is further to increment the shortstream counter in response to a determination that the sublength valuehas not exceeded the short stream threshold.

In an example, the prefetch circuit is further to, for each entry of theplurality of entries: maintain a state machine comprising aninitialization state, a detection state, a first stride state, and asecond stride state; and adjust the sublength values using the statemachine.

Embodiments may be implemented in code and may be stored on anon-transitory storage medium having stored thereon instructions whichcan be used to program a system to perform the instructions. Embodimentsalso may be implemented in data and may be stored on a non-transitorystorage medium, which if used by at least one machine, causes the atleast one machine to fabricate at least one integrated circuit toperform one or more operations. The storage medium may include, but isnot limited to, any type of disk including floppy disks, optical disks,solid state drives (SSDs), compact disk read-only memories (CD-ROMs),compact disk rewritables (CD-RWs), and magneto-optical disks,semiconductor devices such as read-only memories (ROMs), random accessmemories (RAMs) such as dynamic random access memories (DRAMs), staticrandom access memories (SRAMs), erasable programmable read-only memories(EPROMs), flash memories, electrically erasable programmable read-onlymemories (EEPROMs), magnetic or optical cards, or any other type ofmedia suitable for storing electronic instructions.

It is contemplated that various combinations of the above examples arepossible. Embodiments may be used in many different types of systems.For example, in one embodiment a communication device can be arranged toperform the various methods and techniques described herein. Of course,the scope of the present invention is not limited to a communicationdevice, and instead other embodiments can be directed to other types ofapparatus for processing instructions, or one or more machine readablemedia including instructions that in response to being executed on acomputing device, cause the device to carry out one or more of themethods and techniques described herein.

References throughout this specification to “one embodiment” or “anembodiment” mean that a particular feature, structure, or characteristicdescribed in connection with the embodiment is included in at least oneimplementation encompassed within the present invention. Thus,appearances of the phrase “one embodiment” or “in an embodiment” are notnecessarily referring to the same embodiment. Furthermore, theparticular features, structures, or characteristics may be instituted inother suitable forms other than the particular embodiment illustratedand all such forms may be encompassed within the claims of the presentapplication. As used herein, “in response to” refers to a directcause-and-effect relationship.

While the present invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present invention.

What is claimed is:
 1. A processor comprising: a prefetch history arraycomprising a plurality of entries corresponding to prefetch addresses,the plurality of entries comprising a plurality of sublength values,each entry of the plurality of entries comprising a sublength value,wherein each sublength value is a numeric value indicating a frequencythat a stride is repeated for a corresponding prefetch address; and aprefetch circuit to: for each entry of the plurality of entries, adjustthe sublength value based on stride matches for an address of the entry;compare each of the plurality of sublength values to a short streamthreshold; increment a short stream counter for each of the plurality ofsublength values that has not exceeded the short stream threshold,wherein the short stream counter is distinct from the plurality ofentries in the prefetch history array; decrement the short streamcounter for each of the plurality of sublength values that has exceededthe short stream threshold; determine whether the short stream counterhas exceeded a throttling threshold; and in response to a determinationthat the short stream counter has exceeded the throttling threshold,throttle a prefetch level of all prefetches by the prefetch circuit. 2.The processor of claim 1, the prefetch circuit further to: in responseto a determination that the short stream counter has not exceeded thethrottling threshold, reduce throttling of the prefetch level of theprefetch circuit.
 3. The processor of claim 1, wherein each entry of theplurality of entries comprises information related to a state machineincluding an initialization state, a detection state, a first stridestate, and a second stride state.
 4. The processor of claim 3, whereineach entry of the plurality of entries further comprises an instructionpointer address and a stride value.
 5. The processor of claim 3, theprefetch circuit further to, for each entry of the plurality of entries:at a first point in time, in response to a detection of a stride matchwhen the state machine is in the detection state, transition the statemachine to the first stride state and set the sublength value to aninitial value; and at a second point in time, in response to a detectionof a stride match when the state machine is in the first stride state,increment the sublength value by one.
 6. The processor of claim 5, theprefetch circuit further to, for each entry of the plurality of entries:at a third point in time, in response to a detection of a stridemismatch when the state machine is in the first stride state, transitionthe state machine to the second stride state and set the sublength valueto a value of one; at a fourth point in time, in response to a detectionof a stride match when the state machine is in the second stride state,transition the state machine to the first stride state and set thesublength value to a value of two; and at a fifth point in time, inresponse to a detection of a stride mismatch when the state machine isin the second stride state, transition the state machine to thedetection state and set the sublength value to a value of zero.
 7. Theprocessor of claim 3, wherein each entry of the prefetch history arrayincludes a state field, wherein the state field indicates a currentstate of the state machine.
 8. A method comprising: maintaining, by aprefetch circuit of a processor, a prefetch history array comprising aplurality of entries, the plurality of entries comprising a plurality ofsublength values, each entry comprising a sublength value, wherein eachsublength value is a numeric value indicating a frequency that a strideis repeated for a corresponding prefetch address; for each entry of theplurality of entries, the prefetch circuit adjusting the sublength valuebased on whether loads associated with the entry have stride matches;the prefetch circuit comparing each of the plurality of sublength valuesto a short stream threshold; the prefetch circuit incrementing a shortstream counter for each of the plurality of sublength values that hasnot exceeded the short stream threshold, wherein the short streamcounter is distinct from the plurality of entries; the prefetch circuitdecrementing the short stream counter for each of the plurality ofsublength values that has exceeded the short stream threshold; theprefetch circuit determining whether the short stream counter hasexceeded a throttling threshold; and the prefetch circuit increasingthrottling of a prefetch level of all prefetches by the prefetch circuitin response to a determination that the short stream counter hasexceeded the throttling threshold.
 9. The method of claim 8, furthercomprising, subsequent to increasing throttling of the prefetch level:updating the short stream counter; determining that the updated shortstream counter does not exceed the throttling threshold; and in responseto determining that the updated short stream counter does not exceed thethrottling threshold, decreasing throttling of the prefetch level of theprefetch circuit.
 10. The method of claim 8, wherein maintaining theprefetch history array further comprises, for each entry of theplurality of entries: maintaining a state machine comprising aninitialization state, a detection state, a first stride state, and asecond stride state; transitioning the state machine based on stridematches; and adjusting the sublength value based on transitions in thestate machine.
 11. The method of claim 10, wherein each entry of theprefetch history array includes a state field, wherein the state fieldindicates a current state of the state machine.
 12. A system comprising:a processor including a prefetch circuit to: maintain a prefetch historyarray comprising a plurality of entries, the plurality of entriescomprising a plurality of sublength values, each entry comprising asublength value, wherein each sublength value is a numeric valueindicating a frequency that a stride is repeated for a correspondingprefetch address; adjust the sublength values of the plurality ofentries based on stride matches; compare each of the plurality ofsublength values to a short stream threshold; increment a short streamcounter for each of the plurality of sublength values that has notexceeded the short stream threshold, wherein the short stream counter isdistinct from the plurality of entries in the prefetch history array;decrement the short stream counter for each of the plurality ofsublength values that has exceeded the short stream threshold; determinewhether the short stream counter has exceeded a throttling threshold;and throttle a prefetch level of all prefetches by the prefetch circuitin response to a determination that the short stream counter hasexceeded the throttling threshold; and an external memory coupled to theprocessor.
 13. The system of claim 12, the prefetch circuit further todecrease throttling of the prefetch level of the prefetch circuit inresponse to a determination that the short stream counter has notexceeded the throttling threshold.
 14. The system of claim 12, whereineach entry of the prefetch history array includes a state field, whereinthe state field indicates a current state of a state machine associatedwith each entry of the prefetch history array.
 15. The system of claim14, the prefetch circuit further to, for each entry of the plurality ofentries: maintain the state machine associated with the entry based onstrides associated with the entry; update the state field to indicatethe current state of the state machine, wherein the state machine is totransition between an initialization state, a detection state, a firststride state, and a second stride state; and adjust the sublength valuesusing the state machine.